Process for the production of cellulose shaped bodies, bodies produced by this process and the use thereof

ABSTRACT

Process for the production of cellulose shaped bodies through the precipitation of a cellulose solution containing cellulose dissolved in an amine oxide/water system in a precipitation bath, wherein the solution contains additional cellulose fibers.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national application of internationalapplication serial No. PCT/DE97/01527 filed Jul. 15, 1997, which claimspriority to German Serial No. 196 33 405.5 filed Aug. 19, 1996.

The invention relates to cellulose mouldings which are produced byextruding a solution of cellulose in amine oxides and are reinforced bycellulose fibres, and to a process for their production, and also totheir use.

Cellulose mouldings made from recycled cellulose material arepredominantly produced by the known viscose process. Due to the highenvironmental pollution associated with this process, and theconsiderable capital expenditure, considerable efforts are currentlybeing made worldwide to replace the viscose process with alternativeprocesses. A promising process in relation to the production ofcellulose fibres is the spinning of solutions of the cellulose in amineoxides. It is, known from DE 28 30 685 and also from DD 218 121 thatcellulose is soluble in an N-methylmorpholine-N-oxide (NMMNO)/watersystem, and can be processed by spinning into a precipitation bathcomposed mostly of aqueous NMMNO solution, to give textile fibres.Products produced by this process are already on the market.

Processes for producing nonfibrous cellulose mouldings from NMMNOsolutions, in particular films as packaging of food or drink and alsospecifically in the form of blown films as sausage casings, are likewiseknown. In EP 0 662 283 and WO 95/07811 the blown film is taken off via amandrel and/or via an apparatus composed of a number of discs located inthe area of the air gap between annular die and precipitation bath. Inthe process described in DE 44 21 482 the film bubble emerging from theannular die is stabilized and expanded by the pressure of the column ofliquid present in its interior and of the column of air thereabove. Thisprocess is therefore very similar to the known blown-film process, whichis used in particular in producing films from thermoplastics.

The material properties of mouldings made from a polymeric material arefrequently improved by producing a composite which is composed of apolymeric matrix and a fibre material. Cellulose films, specificallysausage casings, are frequently reinforced with paper or a nonwoven orwoven fabric (DE 23 38 418). This hinders, inter alia, easy propagationof existing fractures, and substantially balances out any strengthdifferences longitudinally and transversely to the direction in whichthe machine is running. However, the production of composites of thistype is relatively complicated, in particular when the amine oxideprocess is used.

Starting from this point, the object of the present invention is toprovide a process which can produce cellulose mouldings with improvedstrength properties and which, in particular, also has a favourableeffect on the properties of cellulose films.

The object is achieved in relation to the process by the characterizingfeatures of Claim 1, and in regard to the mouldings themselves by thecharacterizing features of Claim 9. Advantageous embodiments are givenin the subclaims. The use of the cellulose films produced according tothe invention is characterized in Patent Claim 11.

The novel process features a precipitating solution, a cellulosedissolved in an amine oxide/water system, which additionally comprisescellulose fibres, preferably short fibres. Extrusion/precipitation ofthis mixture produces a fibre-reinforced composite material. Thiscomposite made from highly oriented cellulose fibres in a monoaxially orbiaxially oriented cellulose matrix features increased strength andcontrollable anisotropic mechanical properties.

In composites in which fibres have been embedded into a polymer matrix,there is frequently the problem that the adhesive forces between thefibre and matrix are very low and therefore the desired strength is notachieved. The required adhesion between fibre and matrix is frequentlyonly achieved by using coupling agents, and this is associated withadditional cost in the production process. This, problem does now notarise in the novel process, since the fibres in the cellulose solutionbecome slightly dissolved and/or swollen at the surface, and aretherefore embedded firmly into the cellulose matrix during coagulation.It has proven useful here for the proportion of the fibres in the totalcontent of the cellulose to be at least 5% and at most 90% , preferablyfrom 20 to 60% . The cellulose solution comprising cellulose fibres maybe obtained by introducing additional fibres into the cellulose solutionor else by incomplete dissolution of the cellulose during preparation ofthe cellulose fibres.

Complete dissolution of the fibers introduced can be prevented byreducing the capability of the NMMNO/water/cellulose system to dissolvemore cellulose. It can be seen from the phase diagram in FIG. 1 thatthis capability can be reduced by lowering the temperature and/orincreasing the proportion of water in the solution. According to theinvention, this can also control the degree of swelling and/or ofsurface dissolution of the fibers introduced into the solution. Thisgives another way of varying the properties of the moldings. Theseadvantages do not exist in the viscose process, since here thenon-derivatized cellulose is not dissolved. In FIG. 1, area Aillustrates complete solution of the cellulose fibers. Area Billustrates irreversible swelling of the cellulose fibers. Area Cillustrates reversible swelling of the cellulose fibers. Area Dillustrates no alteration of the cellulose fibers.

The novel process can be used either as a casting process or else inextrusion.

The process is in particular also suitable for producing blown films andflat films.

Practically all types of short cellulose fibre may be used for thecellulose/cellulose fibre composite, for example chemical pulps,recycled fibre materials or natural fibres, e.g. cotton linters, flax,hemp, bast, jute, sisal, ramie or manila. It is, of course, particularlyadvantageous here to use high-strength fibres. Depending on the fibrethickness, the fibre length is preferably in the range from a few μm toa number of mm. It is particularly favourable to use fibres with a verylow titre, firstly due to the large specific surface area of the fibreand secondly because in film production the fibre diameter is directlyrelated to the minimum achievable film thickness. According to theinvention, therefore, the exceptionally thin and high-strength fibres ofbacterial cellulose are particularly well suited for fibre-reinforcementof the cellulose mouldings, specifically of the films.

The novel process is particularly suitable for producing blown filmsusing a film-blowing process. For this, a blown film is produced byextrusion through an annular die. A process of this type is described inthe abovementioned DE 44 21 482. These disclosures are expresslyincorporated herein by reference.

The mouldings produced by this process have an excellent modulus ofelasticity from 1200 to 15,000 MPa. These films are particularlysuitable for packaging food or drink. The moduli of elasticity of themouldings depend on the process and for those produced by the castingprocess are in the lower range, preferably from 1200 to 6000 MPa, andare in the range from 5000 to 10,000 MPa for mouldings produced byextrusion processes.

The invention is described in more detail below using working examples.

EXAMPLE 1 1st Comparative Example

Water is added to a solution of 9% of cellulose in NMMNO monohydrate(ratio NMMNO/water=87/13) until the NMMNO/water ratio is 82/18. Thesolution is processed to give a cast film, by spreading out on a glassplate followed by coagulation in water. After drying the film has amodulus of 810 MPa.

EXAMPLE 2

As Example 1 with addition of 30% of ground cellulose, based on thedissolved cellulose, to the cellulose solution. After drying, the filmhas a modulus of 1240 MPa.

EXAMPLE 3

As Example 2 with addition of flax instead of cellulose to the cellulosesolution. After drying, the film has a modulus of 2350 MPa.

EXAMPLE 4

As Example 2 with addition of bacterial cellulose instead of celluloseto the cellulose solution. After drying, the film has a modulus of 1620MPa.

EXAMPLE 5

As Example 3 with reduction of the water content of the solution to anNMMNO/water ratio of 85/15. After drying, the film has a modulus of 2100MPa.

EXAMPLE 6 2nd Comparative Example

A solution corresponding to Example 1 is extruded through an annular dievia an air gap into an aqueous precipitation bath. After drying, theblown film has a modulus of 1900 MPa.

EXAMPLE 7

As Example 6 with addition of 30% of ground cellulose, based on thedissolved cellulose, to the cellulose solution. After drying, the filmhas a modulus of 5400 MPa.

What is claimed is:
 1. A process for producing blown films comprisingthe steps of forming a cellulose and aqueous amine oxide solution,introducing additional fibers into the solution, and producing ablown-film by extrusion through an annular die wherein the degree ofswelling of the additional fibers is controlled by lowering thetemperature and/or increasing the proportion of water in the solution.2. The process according to claim 1 wherein the proportion of the fibersin the total content of the cellulose in the solution is at least 5% andat most 90%.
 3. The process according to claim 2 wherein the fibersintroduced into the cellulose solution are selected from the groupconsisting of chemical pulp, recycled fiber material and natural fibers.4. The process according to claim 1 wherein the proportion of the fibersrelative to the total cellulose content is at least 20% and at most 60%.5. The process according to claim 1 wherein the fibers introduced intothe cellulose solution are selected from the group consisting ofchemical pulp, recycled fiber material and natural fibers.
 6. Theprocess according to claim 1 wherein the fibers are bacterial cellulosefibers.
 7. The process according to claim 6 wherein the proportion ofthe fibers in the total content of the cellulose in the solution is atleast 5% and at most 90%.
 8. The process according to claim 6 whereinthe proportion of the fibers relative to the total cellulose content isat least 20% and at most 60%.